You use erstwhile to describe someone that used to be the type of person indicated, but no longer is.
例句
Erstwhile workers may have become managers...过去的工人可能已经成了经理。He fled to America with Phyllis Burton, an erstwhile friend of his wife's.他和他妻子以前的一个朋友菲莉丝·伯顿一起逃往美国。
英英词典释义
Adjective
1. belonging to some prior time;
"erstwhile friend""our former glory""the once capital of the state""her quondam lover"